This invention relates to a direct current power supply for manual arc welding having a steeply drooping, adjustable characteristic. In this context, the expression "steeply drooping" should be understood to indicate that the short circuit current exceeds the arc current by not more than 50 %. More particularly, the invention relates to a power supply of the type comprising a polyphase transformer, a polyphase rectifier system connected to the secondary of said polyphase transformer, said rectifier system comprising a set of triggered rectifier valves connected one in series with each secondary phase circuit of the polyphase transformer, a pair of welding current conductors connected to the output of said polyphase rectifier system, means for controlling the firing angle of the triggered rectifier system in response to a direct current control signal, and signal generating means for producing said direct current control signal, said signal generating means comprising
Means for producing an adjustable direct current reference signal, PA1 Means including a welding current sensing means for producing a welding current feed-back direct current signal, and, PA1 Summing means for combining said reference signal and said welding current feed-back signal into a compound signal constituting the control signal aforementioned, said feedback signal being supplied to said summing means in opposing relationship to said reference signal. PA1 a. means for producing an adjustable direct current reference signal, including manually operable means for adjusting said reference signal, PA1 b. means including a welding current sensing means for producing a welding current feed-back D.C. signal equal to the welding current multiplied by a first factor of proportionality, PA1 c. means including a welding voltage sensing means for producing a welding voltage feed-back D.C. signal equal to the welding voltage multiplied by a second factor of proportionality, PA1 d. summing means for combining said reference signal, said welding current feed-back signal and said welding voltage feed-back signal into a compound signal constituting the control signal aforementioned, both of said feed-back signals being supplied to said summing means in opposing relationship to said reference signal, PA1 e. slope adjustment means comprising means for adjusting the proportion between said first and second factors of proportionality, and, PA1 f. means linking said manually operable means for adjusting the reference signal and said proportion adjusting means to provide automatically a desired correlation between the slope of the characteristic and the reference signal setting. PA1 a. means for producing an adjustable D.C. reference signal, including manually operable means for adjusting said reference signal, PA1 b. means including a welding current sensing means for producing a welding current fed-back D.C. signal equal to the welding current multiplied by a first factor of proportionality, PA1 c. means including a welding voltage sensing means for producing a welding voltage feed-back D.C. signal equal to the welding voltage multiplied by a second factor of proportionality, PA1 d. a capacitor connected in series with a resistor, means including a welding voltage sensing means for submitting said series connection to potential variations proportional to the variations of the welding voltage, and means for producing a transient feed-back signal equal to the voltage appearing across said resistor multiplied by a third factor of proportionality, PA1 e. summing means for combining said reference signal, said welding current feed-back signal, said welding voltage feed-back signal and said transient feed-back signal into a compound signal constituting the control signal aforementioned, said welding current feed-back signal and said welding voltage feed-back signal being supplied to said summing means in opposing relationship to said reference signal, transient feed-back signals caused by discharge of said capacitor being supplied to said summing means in aiding relationship to said reference signal, PA1 f. transient slope adjusting means comprising means for adjusting the proportion between said first and said third factors of proportionality, and, PA1 g. means linking said manually operable means for adjusting the reference signal and said proportion adjusting means to provide automatically a desired correlation between the transient slope of the characteristic and the reference signal setting.
In a welding power supply of this kind described in the U.S. Pat. No. 3,530,359, the adjustable D.C. reference signal is obtained by the combining of two component signals, both of which are individually adjustable. More particularly, one adjusting member is provided for the first component, while two adjusting members independent of each other and of said first-mentioned adjusting member are provided for the second component. One of said two last-mentioned adjusting members also serves to control the slope of the characteristic through adjustment of the factor of proportionality between the welding current feed-back signal and the welding current. Consequently, the proper adjustment of the apparatus involves the manipulation of three independent controls, which tends to confuse the operator. Operators therefore tend to leave the slope control alone, so that the power supply operates with a constant slope throughout the current range. This mode of operation necessarily results in some sacrifice of welding properties in part of the welding current range.